This invention relates to a novel copolymer of chlorotrifluoroethylene, a fatty acid ester and a glycidyl ether, which is soluble in various organic solvents and is curable.
Polymers of some fluorocompounds have provided synthetic resins which possess good mechanical properties and excellent heat resistance, chemical resistance and weather resistance. As one field of applications of fluororesins, employment thereof as paint vehicles has been developed with a view to utilizing their excellent chemical resistance and weather resistance for producing maintenance-free coating films. For example, polytetrafluoroethylene, polychlorotrifluoroethylene and vinylidene fluoride base copolymers have attracted interest as paint vehicles, and also it has been developed to modify a conventional synthetic resin base paint by the addition of a certain fluororesin. Paint or coating films containing a fluororesin are noteworthy in lubricating and nonadherent properties too.
In the early days of development fluororesin base paints were almost limited to powder paints and dispersions in water or organic liquid. In applications of these paints heating to a temperaure above the melting point of the employed fluororesin is an indispensable requisite for formation of a uniform paint film, so that a high temperature baking treatment which calls for skill has to be performed by experts. To expand practical applicabilities of fluororesin base paints, recently much attention has been directed to fluororesin base paints of the solvent-thinned type which do not require baking treatment for curing and which can easily be used on the site of mechanical manufacture or building work.
To obtain fluororesins that are soluble in practicable organic solvents and useful as vehicles in solvent-thinned paints, usually it is necessary to reduce crystallinity of fluorine-containing polymers by certain means such as copolymerization to thereby accomplish internal plastization. Furthermore, there are some other problems to be resolved in producing a practical paint by using a fluororesin which is rendered soluble. For instance, the problems will include how to retain a desirable degree of rigidity or shear modulus in the soluble fluororesin, how to control the molecular weight of the fluororesin with a view to desirably adjusting the viscosity of the paint and how to select and control the kind and amount of functional groups which must be introduced into the soluble fluororesin in order to obtain a paint that is curable, recoatable and resistant to chemicals. Cost of production also has to be taken into consideration. It is not easy to reach balanced solution for all of these problems. As soluble and curable fluororesins for use in paints, GB No. 2,081,727A shows copolymers of fluoroolefin, cyclohexyl vinyl ether, alkyl vinyl ether and hydroxyalkyl vinyl ether and JP-A 57-34108 copolymers of fluoroolefin, cyclohexyl vinyl ether and glycidyl vinyl ether.
It is reported in GB No. 888,014 and in J. Polymer Science, Vol. 11, No. 5 (1953), 455 that a copolymer of chlorotrifluoroethylene and a vinyl ester of fatty acid exhibits high transparency over a wide range of wavelength and possesses high tensile strength and excellent impact resistance and can relatively easily be dissolved in organic solvents by moderate heating. If a solution of this copolymer is used as a paint or coating composition it will be possible to obtain a coating film that is hard, transparent and glossy. However, this solution lacks recoatability since the copolymer is not curable.
GB No. 2,163,756A (and corresponding U.S. Pat. No. 4,631,326) shows a copolymer of chlorotrifluoroethylene, a vinyl or isopropenyl ester of fatty acid and a hydroxyl-containing allyl ether. This copolymer is soluble in various organic solvents and is curable at relatively low temperatures with a curing agent that reacts with active hydrogen. A solution of this copolymer serves as a paint or coating composition which provides a coating film excellent as a fluororesin film. Coating films formed of this copolymer exhibit good adhesion to metal surfaces, but some unsatisfaction remains in adhesion of the same coating films to glass surface.